1. Field of the Invention
The present invention relates to a signal processing apparatus for selectively discriminating various input signals of different frequencies in the waveform of rectangular pulses with binary truth values of "1" and "0" or in the waveform of general alternating current and processing an output signal to specify the frequency and kind of each input signal. And more particularly, it relates to an apparatus capable of multiplying or dividing the frequency of each input signal and producing, through a band-pass filter, an output signal to specify the frequency of the input signal.
2. Prior Art
In the ordinary signal processing apparatus designed for selectively discriminating a variety of input signals of different frequencies and producing an output signal to specify the frequency of each input signal being actually received, it is generally customary that the input signals are introduced in parallel to a plurality of band-pass filters provided respectively in accordance with the kind of input signals and adapted to permit passage of signals of the corresponding frequencies so that the input signal being received is selectively discriminated with respect to the frequency thereof, and a rectifier circuit is provided in a stage posterior to each of the band-pass filters so as to rectify and smooth the output signal of the associated band-pass filter individually, thereby producing an output signal having binary truth values of "1" and "0".
However, since such signal processing apparatus needs to be equipped with a processing circuit including at least band-pass filters and rectifier circuits for the entire kind of input signals to be processed, it is unavoidable that the apparatus becomes expensive and dimensionally bulky. And another disadvantage has also been existent therefore that each band-pass filter comes to be large particularly in case the input signal thereto is in a low frequency range.